/*
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at 
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
using System;

namespace org.apache.commons.pool
{

    /**
     * A "keyed" pooling interface.
     * <p>
     * A keyed pool pools instances of multiple types. Each
     * type may be accessed using an arbitrary key.
     * </p>
     * <p>
     * Example of use:
     * <pre style="border:solid thin; padding: 1ex;"
     * > Object obj = <code style="color:#00C">null</code>;
     * Object key = <code style="color:#C00">"Key"</code>;
     *
     * <code style="color:#00C">try</code> {
     *     obj = pool.borrowObject(key);
     *     <code style="color:#0C0">//...use the object...</code>
     * } <code style="color:#00C">catch</code>(Exception e) {
     *     <code style="color:#0C0">// invalidate the object</code>
     *     pool.invalidateObject(key, obj);
     *     <code style="color:#0C0">// do not return the object to the pool twice</code>
     *     obj = <code style="color:#00C">null</code>;
     * } <code style="color:#00C">finally</code> {
     *     <code style="color:#0C0">// make sure the object is returned to the pool</code>
     *     <code style="color:#00C">if</code>(<code style="color:#00C">null</code> != obj) {
     *         pool.returnObject(key, obj);
     *     }
     * }</pre>
     * </p>
     * <p>
     * {@link KeyedObjectPool} implementations <i>may</i> choose to store at most
     * one instance per key value, or may choose to maintain a pool of instances
     * for each key (essentially creating a {@link java.util.Map Map} of
     * {@link ObjectPool pools}).
     * </p>
     *
     * <p>See {@link BaseKeyedObjectPool} for a simple base implementation.</p>
     *
     * @param <K> the type of keys in this pool
     * @param <V> the type of objects held in this pool
     * 
     * @author Rodney Waldhoff
     * @author Sandy McArthur
     * @version $Revision: 1222396 $ $Date: 2011-12-22 14:02:25 -0500 (Thu, 22 Dec 2011) $
     * @see KeyedPoolableObjectFactory
     * @see KeyedObjectPoolFactory
     * @see ObjectPool
     * @see BaseKeyedObjectPool
     * @since Pool 1.0
     */
    public interface KeyedObjectPool<K, V>
    {
        /**
         * Obtains an instance from this pool for the specified <code>key</code>.
         * <p>
         * Instances returned from this method will have been either newly created with
         * {@link KeyedPoolableObjectFactory#makeObject makeObject} or will be a previously idle object and
         * have been activated with {@link KeyedPoolableObjectFactory#activateObject activateObject} and
         * then validated with {@link KeyedPoolableObjectFactory#validateObject validateObject}.
         * <p>
         * By contract, clients <strong>must</strong> return the borrowed object using
         * {@link #returnObject returnObject}, {@link #invalidateObject invalidateObject}, or a related method
         * as defined in an implementation or sub-interface,
         * using a <code>key</code> that is {@link Object#equals equivalent} to the one used to
         * borrow the instance in the first place.
         * <p>
         * The behaviour of this method when the pool has been exhausted
         * is not strictly specified (although it may be specified by implementations).
         * Older versions of this method would return <code>null</code> to indicate exhaustion,
         * newer versions are encouraged to throw a {@link NoSuchElementException}.
         *
         * @param key the key used to obtain the object
         * @return an instance from this pool.
         * @throws IllegalStateException after {@link #close close} has been called on this pool
         * @throws Exception when {@link KeyedPoolableObjectFactory#makeObject makeObject} throws an exception
         * @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance
         */
        V borrowObject(K key);// throws Exception, NoSuchElementException, IllegalStateException;

        /**
         * Return an instance to the pool.
         * By contract, <code>obj</code> <strong>must</strong> have been obtained
         * using {@link #borrowObject borrowObject}
         * or a related method as defined in an implementation
         * or sub-interface
         * using a <code>key</code> that is equivalent to the one used to
         * borrow the instance in the first place.
         *
         * @param key the key used to obtain the object
         * @param obj a {@link #borrowObject borrowed} instance to be returned.
         * @throws Exception 
         */
        void returnObject(K key, V obj);// throws Exception;

        /**
         * <p>Invalidates an object from the pool.</p>
         * 
         * <p>By contract, <code>obj</code> <strong>must</strong> have been obtained
         * using {@link #borrowObject borrowObject} or a related method as defined
         * in an implementation or sub-interface using a <code>key</code> that is
         * equivalent to the one used to borrow the <code>Object</code> in the first place.</p>
         *
         * <p>This method should be used when an object that has been borrowed
         * is determined (due to an exception or other problem) to be invalid.</p>
         *
         * @param key the key used to obtain the object
         * @param obj a {@link #borrowObject borrowed} instance to be returned.
         * @throws Exception 
         */
        void invalidateObject(K key, V obj);// throws Exception;

        /**
         * Create an object using the {@link KeyedPoolableObjectFactory factory} or other
         * implementation dependent mechanism, passivate it, and then place it in the idle object pool.
         * <code>addObject</code> is useful for "pre-loading" a pool with idle objects
         * (Optional operation).
         *
         * @param key the key a new instance should be added to
         * @throws Exception when {@link KeyedPoolableObjectFactory#makeObject} fails.
         * @throws IllegalStateException after {@link #close} has been called on this pool.
         * @throws UnsupportedOperationException when this pool cannot add new idle objects.
         */
        void addObject(K key);// throws Exception, IllegalStateException, UnsupportedOperationException;

        /**
         * Returns the number of instances
         * corresponding to the given <code>key</code>
         * currently idle in this pool (optional operation).
         * Returns a negative value if this information is not available.
         *
         * @param key the key to query
         * @return the number of instances corresponding to the given <code>key</code> currently idle in this pool or a negative value if unsupported
         * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
         */
        int getNumIdle(K key);// throws UnsupportedOperationException;

        /**
         * Returns the number of instances
         * currently borrowed from but not yet returned
         * to the pool corresponding to the
         * given <code>key</code> (optional operation).
         * Returns a negative value if this information is not available.
         *
         * @param key the key to query
         * @return the number of instances corresponding to the given <code>key</code> currently borrowed in this pool or a negative value if unsupported
         * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
         */
        int getNumActive(K key);// throws UnsupportedOperationException;

        /**
         * Returns the total number of instances
         * currently idle in this pool (optional operation).
         * Returns a negative value if this information is not available.
         *
         * @return the total number of instances currently idle in this pool or a negative value if unsupported
         * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
         */
        int getNumIdle();// throws UnsupportedOperationException;

        /**
         * Returns the total number of instances
         * current borrowed from this pool but not
         * yet returned (optional operation).
         * Returns a negative value if this information is not available.
         *
         * @return the total number of instances currently borrowed from this pool or a negative value if unsupported
         * @throws UnsupportedOperationException <strong>deprecated</strong>: when this implementation doesn't support the operation
         */
        int getNumActive();// throws UnsupportedOperationException;

        /**
         * Clears the pool, removing all pooled instances (optional operation).
         * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
         *
         * @throws UnsupportedOperationException when this implementation doesn't support the operation
         */
        void clear();// throws Exception, UnsupportedOperationException;

        /**
         * Clears the specified pool, removing all
         * pooled instances corresponding to
         * the given <code>key</code> (optional operation).
         * Throws {@link UnsupportedOperationException} if the pool cannot be cleared.
         *
         * @param key the key to clear
         * @throws UnsupportedOperationException when this implementation doesn't support the operation
         */
        void clear(K key);// throws Exception, UnsupportedOperationException;

        /**
         * Close this pool, and free any resources associated with it.
         * <p>
         * Calling {@link #addObject addObject} or {@link #borrowObject borrowObject} after invoking
         * this method on a pool will cause them to throw an {@link IllegalStateException}.
         * </p>
         *
         * @throws Exception
         */
        void close();// throws Exception;

        /**
         * Sets the {@link KeyedPoolableObjectFactory factory} the pool uses
         * to create new instances (optional operation).
         * Trying to change the <code>factory</code> after a pool has been used will frequently
         * throw an {@link UnsupportedOperationException}. It is up to the pool
         * implementation to determine when it is acceptable to call this method.
         *
         * @param factory the {@link KeyedPoolableObjectFactory} used to create new instances.
         * @throws IllegalStateException when the factory cannot be set at this time
         * @throws UnsupportedOperationException when this implementation doesn't support the operation
         * [Obsolete] to be removed in pool 2.0
         */
        [Obsolete]
        void setFactory(KeyedPoolableObjectFactory<K, V> factory);// throws IllegalStateException, UnsupportedOperationException;
    }
}